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Microservices

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A brief comparison between a fully service orientated architecture system and a microservices-based system; what each system looks like and how they differ.

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Microservices

  1. 1. Microservices A brief introduction to services and microservices
  2. 2. What is a service? “a mechanism to enable access to one or more capabilities, where the access is provided using a prescribed interface and is exercised consistent with constraints and policies as specified by the service description. “ OASIS Reference Model for Service Oriented Architecture
  3. 3. What is a service? “enable access to one or more capabilities” • Delegated functionality to specialists (no general specialist) “access is provided using a prescribed interface ” • Enforces a distributed architecture, communicating by: • REST, SOAP, AMQP, MSQM, JMS, etc.. ” is exercised consistent with constraints and policies as specified by the service description. ” • Abides by the Service Contract
  4. 4. Service contract Agreement between a service and its consumer that specifies inbound and outbound data as well as the format.
  5. 5. Service contract We have to consider: • Service availability • Service responsiveness • Circuit breaker pattern (if service is not in-memory/remote) • Versioning (heterogeneous or homogeneous) • Security (e.g. authentication) • Transactions (ACID compliance)
  6. 6. Example • Sys AV Scanner • Enables access to a virus scanning service • Access is provided using REST • Responds using JSON • Sys understands the communication protocol “inbound data” • Sys understands the response “outbound data”
  7. 7. Advantages • Scalable • Decoupled • Better control over development, testing and deployment • Easier maintenance • and theoretically is costs less for the business [once it’s up and running]
  8. 8. Heterogeneous & Homogeneous Versioning Homogeneous versioning uses version numbers across the same contract. Heterogeneous versioning uses different types of the same contract.
  9. 9. Disadvantages • Increased ancillary complexity • Increased time cost • ACID is difficult! • Latency • Mitigated by caching or another service / pre-empting requests • Service contracts can be difficult • What happens if a service I need to connect to is no longer available?
  10. 10. Microservices Characteristics & Capabilities
  11. 11. Characteristics: Taxonomy Many functional services and private-shared infrastructure services
  12. 12. Characteristics: Granularity Microservices are small, fine-grained services. They do one thing, and they do it well. • Granularity affects performance! • Service Contract overhead can add 100ms to the total response time • Can impede ACID compliance if services are too granular
  13. 13. Characteristics: Choreography / Orchestration Orchestration: coordination with a central mediator Choreography: coordination without a central mediator Microservices favour orchestration over choreography Too much choreography can lead to higher efferent coupling • The degree to which one component is dependent on other components to complete a single business request
  14. 14. Characteristics: Choreography / Orchestration Don’t be afraid to redefine services in a more coarsely-grained manner!
  15. 15. Characteristics: Topology Microservices have an API layer • Mediator in service orchestration • Server-access façade • Introduces abstraction • Context awareness (single bounded context) • Each service can share or have its own access to the infrastructure layer
  16. 16. Service 1:1 Data store • Eradicates different read/write patterns • Enables true separation between bounded contexts • Logical separation between subdomains • Now you have to consider how services will communicate • (and the CAP theorem)
  17. 17. Capabilities: Heterogeneous Interoperability The ability to integrate different programming languages and platforms • Microservices support protocol-aware-heteronegeous-interopability • Protocol between API layer and service MUST be the same • SOA also supports protocol-agnostic-heterogeneous-interopability • Hallelujah for that protocol-transforming middleware
  18. 18. Microservices vs SOA Contract decoupling Mediation / Routing Protocol Transformation Infrastructure
  19. 19. Contract decoupling • Allow services to consume a message that does not abide to the service contract… the holy grail of abstraction • Message Transformation • Convert XML to JSON • Message Enhancement • Normalise date/time format
  20. 20. Mediation / Routing • Provides the ability to mediate (discover services) and route a request • A service registry typically acts as the central service configuration repository
  21. 21. Protocol Transformation • Enables protocol agnostic heterogenous interopability • Potentially allows service optimisation • Service A can only communicate in SOAP, Service B is much faster at accepting requests in REST
  22. 22. Infrastructure • Microservices are easier to deploy and build • Do not require dedicated enterprise business services (NO ESB/MB) • Microservices can use “lightweight” communication protocols, whereas SOA prefers standards and “heavier” protocols: XML, SOAP
  23. 23. Summary • Loose coupling, high cohesiveness services • API layer coordinates between itself and the microservice • Each service is adequately insular

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